Pyrrole carbonitrile compounds useful as insecticides, acaricides and molluscicides are described in copending patent application Ser. No. 430,601 filed Nov. 6, 1989. These compounds may be prepared by halogenating pyrrole-3-carbonitrile.
Pyrrole-3-carbonitrile is difficult to synthesize. Literature methods such as that reported by A. M. van Leusen et al., Tetrahedron Letters, 5337, (1972) report yields of 10% or less.
M. S. Morales-Rios et al., Tetrahedron, 45, pages 6439-6448 (1989) disclose the preparation of methyl 2-chloropyrrole-3-carboxylate from methyl 2-cyano4,4-dimethoxybutyrate and hydrochloric acid. However, methyl 2-chloropyrrole-3-carboxylate is distinct from the 2-halopyrrole-3-carbonitrile compounds prepared by the process of the present invention.
It is therefore an object of the present invention to provide a new and efficient process for preparing 2-halopyrrole-3-carbonitrile compounds.